Noun project
Free Stuff
When designing icons and illustrations the noun project is a number one place to look for inspiration. As an open-source archive of icons for every topic under the sun (almost) the noun project is a top place to see a massive range of ways to condense a concept into just a few lines and fills.
Of course, as well as inspiration icons can be downloaded and used (with the right accreditation) as pixel or vector files. There are plug-ins available for adobe, figma and sketch making it super comfortable to find icons to use in UI and UX design.